Molecular Engineering in Hole Transport π-Conjugated Polymers to Enable High Efficiency Colloidal Quantum Dot Solar Cells

Organic p-type materials are potential candidates as solution processable hole transport materials (HTMs) for colloidal quantum dot solar cells (CQDSCs) because of their good hole accepting/electron blocking characteristics and synthetic versatility. However, organic HTMs have still demonstrated inferior performance compared to conventional p-type CQD HTMs. In this work, organic pi-conjugated polymer (pi-CP) based HTMs, which can achieve performance superior to that of state-of-the-art HTM, p-type CQDs, are developed. The molecular engineering of the pi-CPs alters their optoelectronic properties, and the charge generation and collection in CQDSCs using them are substantially improved. A device using PBDTTPD-HT achieves power conversion efficiency (PCE) of 11.53% with decent air-storage stability. This is the highest reported PCE among CQDSCs using organic HTMs, and even higher than the reported best solid-state ligand exchange-free CQDSC using pCQD-HTM. From the viewpoint of device processing, device fabrication does not require any solid-state ligand exchange step or layer-by-layer deposition process, which is favorable for exploiting commercial processing techniques.